Elevated levels of 22-carbon non-methylene interrupted fatty acids as a common attribute of surviving juvenile hard clams,

Mercenaria mercenaria, following abrupt temperature decline.

Sixto E. Portilla Graduate Center – Ph.D. Program in Earth and Environmental Sciences

Graduate Center, City University of New York January 28, 2013

The problem of hard clam overwinter mortality

• Unexplained, highly variable, site specific winter mortalities are considered the principle obstacle for the development of aquaculture of this species

• Winter survival of the notata strain is as low as 0% (Gionet et al. 2008) • These losses create an unknown risk to the aquaculture industry

(Bricelj et al. 2007)

Stress response from pre-winter declining temperatures

Changes in fatty acids occurred during 2 phases of temperature decline (Pernet et al. 2006) • 18°C to 12°C • 12°C to 6°C

Stress response from pre-winter declining temperatures

Changes in fatty acids occurred during 2 phases of temperature decline (Pernet et al. 2006) • 18°C to 12°C • 12°C to 6°C:

What are 22:2 NMIs?

• NMI synthesis from 16:0, palmitic acid (Zhukova 1986):

• They have been found in reverse relation to EPA and DHA (Klingensmith 1982)

Why is lipid remodeling important?

Hard clams respond to the stress of thermal decline by regulating cell membrane viscosity according to HVA

• Unsaturated FAs have been linked to lowering viscosity and increasing fluidity of cell membranes with lower temperature

(Synensky 1974)

Experimental design

• Five groups of 1200 juvenile hard clams, Mercenaria mercenaria • Average size 8.1 mm (±0.71 mm)

• Fed diets with varying amounts of EPA and DHA

• Temperature regime provided by water bath drawn from benthic zone of Great South Bay, New York

• Mortality removed and counted daily • FAME were measured by GC biweekly

An unexpected result:

An unexpected result:

EPA and DHA

Conclusions

• The group known as 22:2 NMI fatty acids were a prominent component of the pool of survivors of an abrupt temperature decline

• The only diet devoid of EPA and DHA, Group A, showed a decrease in 22:2 NMIs

• Inadequate levels of EFAs in their natural diet may lead to near total loss of juvenile hard clams

• A follow-up study is being performed to track FAs during mild and even temperature decline • (1°C per 5 days)

• Questions?

EPA and DHA: initial to post